The broad objective of this proposal is to understand to relationship between the carcinogenicity of 3-methylcholanthrene and the activity of benzpyrene hydroxylase. Toward this end a unique mouse colony of approximately 20 inbred strains will be screened for benzpyrene hydroxylase activity in liver, lung, g.i. tract, skin and kidney in order to characterize the colony into high, medium and low enzyme carriers. The inducibility of benzpyrene hydroxylase in these mice will be assessed in vivo after injection of 3-methylcholanthrene and by an in vitro organ culture technique with fetal tissues. Furthermore, the induction of the enzyme will be measured at the 18-20 day fetal and 1-2 day neonatal stages as well as during adulthood. The carcinogenicity of 3-methylcholanthrene and its hydroxylated derivatives will be assessed in newborn mice. The former will be administered in the presence and absence of an inhibitor and inducer of benzpyrene hydroxylase. In this manner, information will be gained relative to the role of this enzyme in carcinogenesis.